Preparation for future photovoltaic?

But you know what moon prices installers sometimes charge for cables. Since I lay all my other cables myself, why should I make an exception specifically for photovoltaics?

You don't know which ones, how many, and how long.

It's also about warranty, I wouldn't include any third-party components in my system either.

Well, as a professional, you should know which cables are there and what they're used for. If they've been there for a while, you do a measurement and know whether they are okay. That doesn't take more than 10 minutes. If it's simply the wrong cable, then of course I wouldn't take the risk either and I agree with you. But many just tell the customer that it doesn't work that way to earn a bit more money.

I have now found out: They must be real solar cables, double insulated, approved, 6 mm2. Two of those. Plus 16 mm2 grounding cable.

Depends on the size and whether power optimizers and/or multi-string solutions are present.

I have found out by now: They have to be real solar cables, double insulated, approved, 6 mm2. Two pieces of those. Plus 16 mm2 grounding cable.

depends on the size and whether power optimizers and/or multi-string solutions are present.

And there are more points. Better lay empty conduits. If you tackle this project at some point, then talk to the providers beforehand that you want to lay the cables yourself. They should tell you which ones they need. That way you are currently best off.

Is it even possible to pull cables in these dimensions afterwards? From the roof to the basement is quite a distance and I can't imagine how to make even a single bend with them.